Fecha de publicación: -- Fuente: Wipo "digitalization" A digital data communication overlay system is disclosed which is overlaid on a predefined frequency band of an existing analog data communication system. The digital data communication overlay system comprises a digital mobile unit and a digital ground station. The digital mobile unit and the digital ground station are configured to transmit and receive spread spectrum digital data communication signals between each other over the same spread spectrum digital channel. This is done by spreading the spread spectrum digital data communication signals over the predefined frequency spectrum of the existing analog data communication system.